The invention relates to a throttle body with a throttle housing made of plastic 1.
Throttle housings of throttle bodies are generally made from aluminum by die casting. However, this has the disadvantage that involved and careful machining of the die casting is required, and there is also the fact that such throttle housings are heavy and have poor corrosion resistance.
Consideration has therefore already been given to producing the throttle housing from plastic by injection molding. Such throttle housings made of plastic have the advantage that they are lighter than aluminum housings, that the production material is less expensive and that inserts, for bearings for example, can be press-fitted in openings formed during the injection-molding process, thus making it either completely unnecessary to machine the molding or significantly reducing the amount of machining required.
However, throttle housings made from plastic have the disadvantage that they may shrink during and after the injection-molding process and may deform after being released from the mold. The same applies to the effects of temperature and forces, especially since such throttle bodies are arranged in the engine compartment of vehicles, where they are subject to very large fluctuations in temperature. If, for example, the engine of the vehicle is not in operation and the outside temperature is low, very low temperatures are reached (e.g. temperatures around freezing point or even below); when the internal combustion engine is operating, on the other hand, a very high temperature (in particular over 100 C.) is reached. Due, in particular, to these large temperature fluctuations, disadvantageous deformations therefore occur in the pivoting rang e of the throttle butterfly, making it impossible to meet the high leakage-air requirements, particularly in the idle position of the throttle butterfly and around the latter. However, it is precisely this range that is particularly important since it exerts a major effect on fuel consumption and the quality of the exhaust gas. It is therefore particularly important that the intake wall of the throttle body should maintain its dimensional accuracy, both under the conditions mentioned and over a prolonged period, in particular a number of years.
DE 43 34 180A1 has therefore already proposed embedding an annular insert into the plastic throttle body, transversely to the intake duct, this insert having angled lugs through which the throttle shaft projects, and the lugs resting by a respective lug surface facing away from the throttle butterfly against a bearing end face of the bearing devices, the said end face facing the throttle butterfly. First of all, this annular insert has the disadvantage, owing to its geometrical design, that it is expensive to manufacture, particularly during the series production of throttle bodies.
However, the essential disadvantage is that the annular insert is completely surrounded by plastic after the injection-molding process and the throttle butterfly thus once more has a large-area internal intake-wall contour made of plastic in its pivoting range. Due to the high requirements as regards protection of the environment (quality of the exhaust gas) and fuel consumption, the required dimensional accuracy is still not guaranteed, even if it is somewhat better, allowing the plastic intake wall to deform, contract and expand despite the annular insert, with the result that the high leakage-air requirements are, as before, not met.
The underlying object of the invention is therefore to improve a throttle body of this kind further so that the requirements made as regards the quality of the exhaust gas and fuel consumption are met but, at the same time, that requirements as regards a uniform response of the internal combustion engine to depression of the accelerator pedal are met. At the same time, the advantages of a plastic throttle body should not be abandoned.
According to the invention, a metal cylinder is provided in the conduit section over at least part of the pivoting range of the throttle butterfly.
Owing to the stability of a metal cylinder, the throttle butterfly is always presented, at least in the relevant part of the pivoting range, with a precisely defined and dimensionally accurate inner wall which changes only negligibly, if at all, in the case of temperature fluctuations and over a prolonged period, and the required dimensional accuracy is thus ensured. The metal cylinder can be inserted into the injection mold and then surrounded with plastic in such a way that its inner wall remains free, thus presenting a metal surface to the throttle butterfly. As an alternative, it is also possible to produce the throttle housing from plastic first and then to insert the metal cylinder. It is also conceivable to produce the metal cylinder from a number of parts, it being possible, for example, for two halves to abut in the plane in which the throttle shaft is situated. It would also be conceivable to cover the inner wall of the metal cylinder with a thin protective layer (composed, for example, of the same plastic of which the throttle housing is composed), the thickness of which has no effect on dimensional accuracy. Such a protective layer is an effective means of preventing the deposition of troublesome particles on the inner wall.
As a development of the invention, the metal cylinder is provided below and/or above the throttle shaft carrying the throttle butterfly, in the direction of flow. It is precisely the area around the plane in which the throttle shaft is arranged that is particularly important since this is the area used to set the idling speed with the throttle butterfly. It is therefore particularly in this area that good dimensional accuracy is required, and this is achieved with the metal cylinder. However, it is also possible for the metal cylinder to extend over a larger pivoting range of the throttle butterfly and, if appropriate, even further.
As a development of the invention, the metal cylinder is formed to hold the bearings for the throttle shaft. This ensures a further increase in strength, thereby also simplifying the production process. The metal cylinder can be produced first and then be provided with the bearings for the throttle butterfly and subsequently surrounded with plastic by molding. Another advantage is to be seen in the fact that different metal cylinders (in particular cylinders of different length and/or different diameter) can be inserted into the same mold for the throttle housing, thereby making it possible to reduce the number of components, in particular the number of molds for the throttle housing.
As a development of the invention, the metal cylinder is also formed to hold further elements of the throttle body, such as elements to hold a throttle-valve potentiometer or a drive motor. Further elements of the throttle body can also include shafts for a gear by means of which the throttle shaft is driven by an electric motor. The metal cylinder can also be provided with holes at which the additional elements, such as a carrier plate for the throttle-valve potentiometer, are screwed on after the production of the throttle housing. The metal cylinder can likewise have stops, for an end position of the throttle butterfly or the throttle butterfly for example.
As a development of the invention, the metal cylinder has an internal contour for the purpose of obtaining a predeterminable characteristic curve for the volume flow as a function of the pivoting of the throttle butterfly. By producing a corresponding metal cylinder from die-cast aluminum or magnesium, for example (other materials and production methods also being possible) and any subsequent machining that may be necessary, the inner contour of the metal cylinder makes it possible to achieve a characteristic curve for the volume flow through the conduit section which is established as a function of the pivoting of the throttle butterfly. An inner contour can, for example, have the effect that virtually no volume flow, if any, takes place through the conduit section in the closed position of the throttle butterfly. In one end position, referred to thus far as the closed position, the conduit section does not necessarily have to be completely closed. Instead, this end position can also be a minimum position, in which a defined leakage air quantity flows through the conduit section. As the throttle butterfly is pivoted further out of the closed position or minimum position, the volume flow increases in a manner dependent on the inner contour used, up to a further end position which, in particular, represents full opening of the conduit section.
In summary, therefore, it can be stated that the advantages of a throttle housing made of plastic (such as low weight and the low cost of materials) are retained by the invention but that the disadvantages with a throttle housing made of plastic, such as inadequate dimensional accuracy, are eliminated by the use of the metal cylinder, allowing the desired characteristic curve to be reliably set and maintained, even in the case of temperature fluctuations and over a long period of time (several years).
The throttle body according to the invention can be what is referred to as a coupled system, in which the throttle butterfly is connected for the power demand to an accelerator pedal via connecting elements such as Bowden cables or the like. It is likewise conceivable in such systems to perform superimposed regulation (in particular idle-speed regulation) in parts of the range (in particular in the idle-speed range) by means of an actuating drive (in particular an electric motor). The throttle body can equally well be employed in so-called drive-by-wire systems, in which the power demand (e.g. actuation of an accelerator pedal) is converted into electrical signals, the signals being fed to a control unit which, in turn, activates an actuating drive which then adjusts the throttle butterfly at least as a function of the power demand and, if appropriate, of further parameters.